1. Field of the Invention
The invention relates to addressable signalling apparatus, and more particularly to an addressable signalling apparatus which may be addressed by a unique address or by an address in which a substitute common unit of address may be used to call a group of such addressable signalling apparatus.
2. Prior Art
Addressable signalling devices have been known for many years. For example, the modern telephone is a common example of such a signalling apparatus.
However, in many instances it is desirable to call a group of similar signalling devices. Previously, this could be achieved mainly by voice signalling.
An object of the invention is to provide a digital signalling apparatus which responds either to a unique address which is transmitted to the apparatus in sequence, or to a common substitute unit of address which permits group calling. A further feature of the invention is to provide such an apparatus which will reset itself if a wrong address unit is received in the sequence of address units being transmitted to the apparatus. Still a further object is to provide a digital signalling apparatus in which an address unit may form a portion of an output signal once the apparatus has been enabled by receipt of its unique address or an address substitute.